edlled by
WALTER A. WOLF Eisenhower College Seneca Falls, New York 13148
Common Grading and Scaling Formulas Donald R. Getzin Department of Chemical Engineering and Chemistry New Jersev Institute of Technolom -" 323 High street Newark, New Jersey 07102 Common grading is desirable, if not essential, in large multi-section courses such as the typical freshman chemistry program, especially when part-time faculty and graduate students are used for part of the teaching. Although most of each student's final total can he based on performance on common examinations, i t is difficult to take into account performance in laboratory and quiz or recitation sections because the various instructors undoubtedly use different grading methods and have different standards. We have overcome this difficulty by using scaled laboratory and recitation scores. A linear scaling formula S = A.P B can he used for scaling each student's arade. P is the student's oercent score compurcil in any rnannw the instrurtt,~chooses, S is the studenr's sc;~lc~l score to IIP ndded into his or her tinnl tartal and A and B are scaling constants for that particular laboratory or recitation section. The constants A and B can be determined in various ways, but we prefer to do so by requiring all sections to have the same re-selected mean scaled score M and standard deviation 2 of the scaled scores from the mean scaled score. Suppose that the mean value of the percent scores P in a particular section ism and the standard deviation of the percent scores from the mean percent score is o. Then when P = m, S = M and when P = m a, S = M 2. Substituting the two points into the scaling formula and solving simultaneously gives A = 2/a and B = M - m.210. The scaling constants will, of course, be different for each section since m and u are different for each section. The method we use for pre-selectingvalues of M and 2 for recitation grades can serve as an example of factors which should be taken into account. For scaled recitation grades based on 100 points, we choose m to be 64 and 2 to he 12. These choices result in M being 1.2 2 above 50 points, which we regard as passing, and 3.0 2 below 100 points. Since f 1.2 2 is the 75% confidence limit, only 12.5% of the students receive scaled recitation scores below 50 points, and. since +3.0 X is rhr 99.7%cmfidenw limit, e~set~rinlly n0studen1 rturiws a sralt4 rwitatiun scow hove 100 pwnts. Mureovrr, the value thusen for \' is dficimtly srnnll that the recitation icwe does nut becomt. the main factor in determining.;I student's tinill grade. One advantage of using scaled grades based on a fixed mean and standard deviation is that the grade "profile" intended by the individual instructor is preserved-only the "average" and "spread" are changed. A contrary argument is that all sections, in spite of some being better than others, are brought to the same level. Our view is that if one section is actually better than another, the difference will appear on the common examinations where it is appropriate.
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794 1 Journal of Chemical Education
